composepost: Normalize rpmdb.sqlite-shm
#4074
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rust/src/composepost.rs
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| @@ -274,6 +274,11 @@ fn postprocess_cleanup_rpmdb_impl(rootfs_dfd: &Dir) -> Result<()> { | |||
| if matches!(name, ".dbenv.lock" | ".rpm.lock") || name.starts_with("__db.") { | |||
| d.remove_file(name)?; | |||
| } | |||
| // SQLite case. Today, it seems to work to remove the WAL, but removing the SHM | |||
| // file causes a runtime error as RPM tries to mutate a read-only database. | |||
| if matches!(name, "rpmdb.sqlite-shm" | "rpmdb.sqlite-wal") { | |||
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In a quick search, I stumbled on https://www.sqlite.org/wal.html which seems to indicate the WAL file is a kind of transaction journal. It wasn't clear to me whether there could be pending transactions not yet committed back that we could be clobbering. Though it looks like librpm force a checkpoint when releasing: https://github.com/rpm-software-management/rpm/blob/c4eb357fe87e7fb7e3895e52cb9dad587b72b2b9/lib/backend/sqlite.c#L207. Hmm, so it should be empty if it was just checkpointed. Do you get reproducible builds if you drop out the WAL file from this match?
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I also don't know much about SQLite, so I reserve the right to be completely wrong about all the above. :)
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A better page is https://www.sqlite.org/walformat.html which talks about the role of the -shm file.
I commented over in rpm-software-management/rpm#2219 but basically the problem seems to be that while sqlite will happily recreate it on start, it will only do that successfully if the directory (and database) isn't read only. I think librpm may be able to fix this by avoiding any database mutation operations when the file is read only.
This code was untested before, I just did one more quick untested thing of just entirely zeroing it but if that doesn't work at some point I'll try digging into a more real solution.
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Out of curiosity, would zero-sized files work for this case (i.e. just truncating the entry)?
The docpage only mentions that the files should be present; it looks like a purely cosmetic placeholder may be good enough (and deterministic/shareable).
In some testing I have using `SOURCE_DATE_EPOCH=0`, this file is now the only thing that differs across builds.
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Filed rpm-software-management/rpm#2219 to track fixing this more properly; I didn't dig deep but I think librpm needs to learn how to handle a read-only rpmdb. |
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In some testing I have using
SOURCE_DATE_EPOCH=0, this file is now the only thing that differs across builds.